In communication applications, dielectric materials with a high quality factor (Q) are desired for making a dielectric layer, because high Q materials have a low rate of energy loss, and therefore oscillations generated in the material last longer without losing the strength. The Q factor of a dielectric material is 1/tan θ where tan θ is the dielectric loss tangent. There is growing demand for dielectric materials with very high Q values greater than 500 or greater than 1,000 for high frequency applications.
High Q materials are generally based on crystalline oxide materials, which sinter at high temperatures of greater than 1000° C. or greater than 1100° C.; for example, titanate powders, which have a K value of greater than about 20. Lower K materials are sought after in electronics industry, including in microelectronics industry, which requires materials with lower signal loss (which is proportional to dielectric constant) or lower delay, as well as reduced cross talk between two conductor lines. Here the requirements are for K less than about 6, preferably less than 4 (even less than 3.8). For this purpose, a number of high Q, low K oxide ceramic materials exist, such as silica (K˜3.8), β-eucryptite (LiAlSiO4) (K˜4.8), sillimanite (Al2O3.SiO2) (K˜5.3), albite (NaAlSi3O8) (K˜5.5), magnesium phosphate (Mg2P2O7) (K˜6.1), aluminum phosphate (AlPO4) (K˜6.1), cordierite (2MgO.2Al2O3.5SiO2) (K˜6.2) and willemite (2ZnO.SiO2) (K˜6.6), wherein the symbol “˜” means “approximately equal to”. However, these crystalline oxide materials have very high sintering temperatures (e.g. greater than 1000° C. or greater than 1100° C.), and may therefore not be compatible with co-firing with other components of an electronic assembly, e.g. silver conductors that are present in electrical assemblies that have a melting temperature of about 960° C.
There are some state of the art LTCC materials with K of 4-12 based on glass added to dielectric systems. The addition of traditional low softening temperature glasses, e.g. ZnO—B2O3-SiO2 glass, to these low K materials can lower the sintering temperature, e.g. less than 1100° C., 950° C. or 900° C., so that it is below the melting temperature of silver conductors that are present in electrical assemblies. However, such addition of traditional glasses also results in either bringing down the Q value, or increasing their dielectric constants of these low K materials, and if not enough glass is added, then the sintering temperature remains high, e.g. above 1100° C., or above 950° C. Accordingly, these systems including glass, and depending on how much glass is added to the system, may suffer from having a K of greater than 4, having a reduced Q value, or have higher sintering temperatures of greater than 950° C., or even greater than 1000° C., or even greater than 1100° C. Because of this, it is quite difficult to produce a material that has a high Q, a K value of less than 4 when measured at high frequencies, and a sintering temperature lower than 900° C. Therefore there exists a need to develop an improved low K dielectric compositions for high frequency applications.
In the state of the art, organic based substrates like FR-4 printed circuit board materials or (CVD or PVD) grown fluorinated glass (SiOF) inorganic glassy materials are used. Even for these materials however, making them in bulk form (e.g. a stand-alone bulk resonator) is not possible with traditional casting or sintering approaches. Moreover, these materials generally operate at lower frequencies (in low MHz) rather than at higher frequencies, cannot handle higher service temperatures, higher energy densities, and have lower mechanical strength.
As such, there is a need to provide improved compositions that address the shortcomings of the previous dielectric materials.